Liquid metal floated gyroscope



April 7, 1964 M. TARASEVJCH ETAL 3,127,776

LIQUID METAL FLOATED GYROSCOPE Filed June 27, 1960 X 5 m m m 0 WWW w WMA T m. &A NN A mm MM United States Patent 3,127,776 LIQUID METAL FLOATEDGYROSCOPE Michael Tarasevich, Glen Cove, N.Y., and Milan A. Telian, SanDiego, Calif., assignors to American Bosch Anna Corporation, acorporation of New York Filed June 27, 1960, Ser. No. 39,089 7 Claims.(Cl. 74-5) The present invention relates to liquid flotation forgyroscopes and has particular reference to liquid metals used therefor.

The concept of flotation of gyros for relieving the load on supportingbearings has received considerable interest during the last decadealthough the history of floated gyros is much older. However, it is onlyrecently that liquids comprising low melting point metals have beenconsidered, discounting the early uses of mercury.

The present invention proposes the use of an alloy of bismuth, indiumand tin, the exact proportions of each being that required to make aeutectic alloy. The metal has many and important advantages over otherflotation fluids previously suggested, such as high thermalconductivity, low thermal coefficient of expansion, non-corrosive and soon but most important is the specific gravity of 7.84 compared to aspecific gravity of 7.87 for stainless steel at a temperature of 85 C.This extremely close matching permits flexibility in design wherebymetal (stainless steel) can be removed from or added to the floatingstructure without upsetting buoyancy. Also, the eutectic alloy ofbismuth, indium, tin is used in preference to other alloys of theseelements to preclude Stratification of elements upon cooling. Furtheradvantages are found in the greater resistance to nuclear radiation overorganic fluids, high lubricity permitting use of jewel bearings insteadof torsion wires, relatively loose temperature control, high angularmomentum to volume ratio and relatively low cost.

These and other advantages will be made clear upon reference to theaccompanying diagram which shows cross section of a typical gyroscopicdevice using the flotation principle.

In the diagram, a gyro wheel 10 is supported for rotation in afluid-tight casing 11 which is suspended in vertical gimbal ring 12about a horizontal axis by horizontal shafts (not shown) perpendicularto the plane of the paper, while the gimbal ring 12 is adapted forrotation about a vertical axis through jewelled bearings 13, 14 andcorresponding shafts 15, 16. The bearings 13, 14 are set into afluid-tight tank 17. The space between casing 11 and tank 17 is filledwith the alloy comprising 32.5% bismuth, 51% indium and 16.5% tin whichis the eutectic alloy of these elements. A diaphragm 18 is inserted inthe wall of tank 17 to permit expansion of the alloy as it is heated tothe operating temperature of about 85 C., the melting point of the alloybeing 61 C. The low thermal coefficient of expansion permits use of thediaphragm in place of the usual expansion bellows.

Convection currents are produced by liquid expansion, as well as bythermal unbalances, as the lighter (expanded) liquid rises and theheavier liquid sinks. When the expansion is limited by a low coeflicientof expansion, the magnitude of the convection currents is kept at asmall value. Convection currents, of course, apply error producingtorques to the gyro, and their reduction is imperative in an accurategyro.

A decrease of specific gravity occurs with expansion resulting in achange in the buoyancy of the casing 11 and gimbal ring 12 in theliquid. The small expansion experienced by the bismuth-indium-tin alloypermits easier control of the buoyancy by tolerating less rigidtemperature controls. The fluid expansion is closely matched 3,127,776Patented Apr. 7, 1964 "ice by the expansion of the casing material whenstainless steel is used.

The high thermal conductivity of the liquid alloy minimizes localizedheating due to outside influences and tends to distribute thetemperature rise evenly throughout the liquid thereby reducing a majorcause of convection currents in the liquid. Also, the high thermalconductivity decreases the warmup time required, conducts heat away fromthe gyro motor and, all in all, insures a uniform temperature.

The specific gravity of the eutectic alloy of bismuthindium-tin at C. is7.84 while the specific gravity of stainless steel at 85 C. is 7.87. Thesignificance of this close matching is that when the casing 11 andgimbal ring 12 are made of stainless steel, changes in their design canbe made freely without disturbing the buoyancy relationship. Also, thegyro wheel can be made of much heavier metal such as tungsten, forexample, without making the specific gravity of the assembly (of thegyro wheel and other components within the casing and the casing itself)greater than the specific gravity of the alloy, 7.84.

The eutectic alloy does not stratify upon cooling; i.e., all theelements solidify at the same temperature. This property is advantageousin starting up the gyro by attaining and maintaining a homogeneousliquid as soon as the metal becomes liquified. Therefore, added warmuptime to obtain a proper mixture is not required nor are there presentany additional error producing torques during the warmup period whichmight add to the initial settling time.

Other advantages of this alloy are found in (1) its superior lubricitywhich permits use of pivot bearings in place of the more intricate wiresuspensions; (2) its greater resistance to nuclear radiation thanorganic flotation liquids; and (3) its non-corrosive reaction to mostcommon structural metals and materials which permits a wider choice ofmaterials for the various parts of the gyroscope which might come incontact with the flotation liquid.

We claim:

1. Means for supporting a gyroscope comprising a tank, a fluid tightcasing suspended in a gimbal ring in said tank, said gimbal ring beingadapted for rotation about a vertical axis through bearings and afloating medium in said tank between said casing and said tank, saidfloating medium comprising an alloy of bismuth, indium and tin, andhaving a specific gravity of approximately 7.84 at a temperature of 85C.

2. Means for supporting a gyroscope comprising a casing and a floatingmedium between said gyroscope and said casing to thereby float saidgyroscope in said casing, said floating medium comprising an alloy ofapproximately 32.5% bismuth, approximately 51% indium and approximately16.5% tin.

3. Means for supporting a gyroscope comprising a casing and a floatingmedium between said gyroscope and said casing to thereby float saidgyroscope in said casing, said floating medium comprising an eutecticalloy of approximately 32.5% bismuth, approximately 51% indium andapproximately 16.5% tin.

4. Means for supporting a gyroscope comprising a tank, a fluid tightcasing suspended in a gimbal ring in said tank, said gimbal ring beingadapted for rotation about a vertical axis through bearings and afloating medium in said tank between said casing and said tank, saidfloating medium comprising an alloy of approximately 32.5% bismuth,approximately 51% indium and approximately 16.5% tin.

5. Means for supporting a gyroscope comprising a casing with a floatingmedium between said gyroscope and said casing to thereby float saidgyroscope in said casing,

said floating medium comprising an eutectic alloy of bismuth, indium andtin.

6. Means for supporting a gyroscope comprising a casing and a floatingmedium between said gyroscope and said casing to thereby float saidgyroscope in said casing, said floating medium comprising an alloy ofbismuth, indium and tin, said alloy having a specific gravity ofapproximately 7.84.

7. Means for supporting a gyroscope comprising a casing and a floatingmedium between said gyroscope and 10 2,896,455

said casing to thereby float said gyroscope in said casing, saidfloating medium comprising an eutectic alloy of bismuth, indium and tin,said alloy having a specific gravity of approximately 7.84.

References Cited in the file of this patent UNITED STATES PATENTS2,625,045 Brubaker et al Jan. 13, 1953 2,817,974 Muzzey et a1 Dec. 31,1957 Bishop et a1. July 28, 1959

1. MEANS FOR SUPPORTING A GYROSCOPE COMPRISING A TANK, A FLUID TIGHTCASING SUSPENDED IN A GIMBAL RING IN SAID TANK, SAID GIMBAL RING BEINGADAPTED FOR ROTATION ABOUT A VERTICAL AXIS THROUGH BEARINGS AND AFLOATING MEDIUM IN SAID TANK BETWEEN SAID CASING AND SAID TANK, SAIDFLOATING MEDIUM COMPRISING AN ALLOY OF BISMUTH, INDIUM AND TIN, ANDHAVING A SPECIFIC GRAVITY OF APPROXIMATELY 7.84 AT A TEMPERATURE OF85*C.